1. Field of the Invention
The present invention relates to a video camera having therein a microcomputer and its control method.
2. Related Background Art
In a video camera, in order to perform an adjustment of the white balance, a correction of the exposure, and the like, there is used a method whereby a position of a predetermined portion in a picture plane and image signal data in a predetermined range are extracted and the white balance and exposure are corrected to proper states on the basis of those information. To control such a correction and to control the whole photographing operation, hitherto, a microcomputer is built in the video camera.
As a method of extracting the position of a predetermined portion in the picture plane and the image signal data in a predetermined range as mentioned above, there has been known a method whereby a microcomputer calculates the position of a predetermined pixel of an image pickup device by a clock signal and a sync signal from the video camera or by a clock signal of the microcomputer itself or the like, thereby extracting a video signal in a predetermined range of the image pickup device.
As another method, there has been known a method whereby a microcomputer generates data indicative of a predetermined position and a predetermined range of a picture plane to an external circuit and the external circuit automatically calculates the pixel position of an image pickup device on the basis of a clock signal and a sync signal of a video camera, thereby extracting image data.
In the former method in the above conventional methods, however, there is a problem such that since the microcomputer extracts image information at a predetermined position in the picture plane, most of the ability of the microcomputer is expended and the ability to control the other portions in the video camera deteriorates. Even in the case where a circuit is provided in the outside as in the latter method, there is a problem such that in order to monitor the end of extraction of the image information at a predetermined position, the microcomputer needs to monitor the external circuit at a predetermined interval, so that its processing ability similarly deteriorates. Therefore, in case of controlling the operation of the video camera by one microcomputer, there is a problem such that the operation cannot be controlled at a high speed and the operation of each section of the video camera is slow.